The goal of this research is to understand how large, stand-replacing wildfires affect the ecosystem carbon (C) balance of southwestern ponderosa pine forests. The investigators are examining the process of wood decomposition because it accounts for the majority of C loss following fire. They will identify the community structure of wood-decay fungi and observe how the community changes in response to fire and with time since fire. They are using observational and experimental studies in conjunction with molecular techniques to study the fungal communities and connect them to decomposition rates. An understanding of how stand-replacing wildfires alter ecosystem C is critical to formulating C predictions throughout the western U.S. This information is even more significant in light of rising atmospheric carbon dioxide (CO2) levels and climate changes that have led to larger, more frequent catastrophic wildfires. This type of fire emits large amounts of CO2 and leaves a vast legacy of dead wood, which releases CO2 long after the fire. Although it is known that wood decay fungi are a major component of C cycles, the extent that severe fires affect the species composition of these fungi, and how the species composition influences rates of wood decay are poorly understood.
Recent alterations in global climate patterns, including increasing mean temperatures and drought severity, have the ability to trigger large-scale plant die-offs, and are correlated with the rising frequency and amount of area burned by wildfires in the western U.S. In ponderosa pine forests of the Southwest, these large, stand-replacing wildfire events are a relatively new type of disturbance on the landscape; therefore, there is uncertainty surrounding the long-term ecosystem response. We used this ecosystem as a model to study controls on carbon (C) accumulation and release following stand-replacing wildfires to help us understand if, and for how long, wildfires will contribute to increased carbon dioxide concentrations in the atmosphere. We established a 35-year chronosequence of stand-replacing wildfires to investigate the effects of fire on ecosystem processes and C pools over time. We measured nitrogen (N) availability as a potential limitation on net primary production, and, therefore, post-wildfire C accumulation. We also examined post-wildfire C losses in the context of wood decomposition because wood is the predominant C storage vessel following these fires. Specifically, we identified the communities (species composition and number of species) responsible for much of the C released through decomposition. Then we performed laboratory experiments to link the fungal community to the process of decay and ecosystem N cycling. We found that stand-replacing wildfires in these forests were associated with long-term (>30 years) alterations in the species composition of wood-decay fungi. This result may have implications for post-fire decomposition rates (and thus, ecosystem C release) because species composition is known to influence rates of wood decay. In support of this, we also found that the species we observed varied considerably in their ability to decay wood. In particular, the species with one of the lowest rates was also found commonly at the most recent burn. Although more study is required, if this species is widely found to be an earlier colonizer of burned areas, it suggests that there could be substantial differences in the amount of C respired from recently burned areas. Our experimental work demonstrated that the fungal communities from unburned forests generally have a greater capacity to decay wood than those from burned forests. Fungal communities from recent burns differed functionally from those at older burns and unburned forests. Specifically, we observed that C and N availability in the soil limits the wood-decaying activity of fungi in the recent burns. However, this pattern was not reflected in the species composition at the recent burns; in fact, we observed similar fungal communities at the recent and older burns. This demonstrates variability in the function of similar groups of fungal species. Overall, our research has advanced our knowledge of wood-decay fungi communities in southwestern ponderosa pine forests through the use of advanced molecular genetics techniques. Previous knowledge of fungi in these systems was limited to opportunistic surveys of fungal fruiting bodies, which were predominantly from one taxonomic phylum of fungi (Basidiomycota). Our work advances this because we found that fungi from the Ascomycota tend to dominate in wood. This means that the Ascomycota may have a previously underestimated role in wood decomposition. We used several different avenues to disseminate our research findings. In 2010, we had a table at the Flagstaff Festival of Science, which is a community-wide series of events to promote science. We had locally-collected sporocarps available, as well as microscopic viewing of fungi growing in culture. We had handouts available that explained the importance of fungi in ecosystem functioning, and we gave away "spore print kits" containing materials and instructions for making a spore print (an essential tool for sporocarp identification). Additionally, we presented several aspects of our findings to the scientific community at the Ecological Society of America annual meeting in 2010 and 2012. We also submitted a manuscript for publication (currently in peer review), and we have plans to work on two more manuscripts from these projects. Finally, our research provided valuable scientific training opportunities to a graduate (Valerie Kurth) and an undergraduate (Nicholas Fransioli) student. Valerie developed laboratory skills in molecular techniques, as well as the computer knowledge necessary to analyze large sequence datasets. Nick conducted one of the laboratory experiments as his senior capstone project in environmental science. He developed skills in the design, execution, and presentation of scientific research.
